Wellsite Geologists: sample questions and answers for the interview

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Q1.? What are important roles and responsibilities of a wellsite geologist on a rig?

Ans. A wellsite geologist serves as a multifaceted expert on an oil rig. Basically he plays three primary roles:

1.??? Expert Geologist: Analyse and interpret geological data, including logs, cuttings, and core samples, to identify and characterize formations, evaluate potential hydrocarbon zones, and assess reservoir quality. As well as identify overpressure zones and estimate formation pressure and advise MW for the safety of operation.

2.??? Operations Coordinator: Oversee geological operations on the rig, coordinating with operations geologis, company man, drillers, directional drillers, logging engineers and other team members to ensure drilling activities align with geological objectives.

3.??? Data And Quality Manager: Ensures that data and logs are being presented on company recommended formats. It is also his essential duty to ensure that all geological data being collected is consistently accurate and meets established standards.

Key responsibilities of a wellsite geologist include:

• Preparing and submitting geological reports and logs on daily basis.
• Interpreting logs and data to provide informed recommendations to the client
• Witnessing and coordinating various operations,?such as wireline logging,?conventional coring,?and directional drilling
• Participating in daily meetings to update the team on geological findings and progress
• Compiling a comprehensive final well report upon completion of the well

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Q2. ?What happens in the pre-job meeting between a wellsite geologist (WSG) and an operations geologist (Ops. Geo) at the client's office?

Ans. The pre-job meeting between a wellsite geologist and an operations geologist is held in client’s office before going to the rig. For wellsite geologist it is a critical opportunity to align on the drilling and geology plan for the well. The Ops Geo will typically provide the WSG with the following information:

• A written drilling and geology plan
• A brief overview of the geology and structural setting of the field
• The objectives of the well
• Any anticipated challenges
• A logging program
• Copies of offset mud logs and wireline logs,?along with any changes in reporting and logging formats

The WSG will review this information and ask clarifying questions. During the discussion the two share their own insights and recommendations based on their experience.

In addition to the technical discussion, the pre-job meeting is also a good opportunity to meet the geology team consisting of geophysicist, Petrophysicist, exploration geologist and the manager etc.

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Q3. What geological points do you cover in your morning briefing during the meeting with town?

Ans. The morning briefing is a daily ritual for the wellsite geologist to inform the geology and drilling teams on the latest geological matters and progress. Key points typically covered in the briefing include:

1.??? Formations drilled or logged in the previous 24 hours

2.??? Oil and gas shows encountered, including net pay thickness

3.??? Structural correlation and interpretation of the well's position within the geological framework

4.??? Directional drilling progress, ensuring the wellbore trajectory aligns with the planned path

5.??? Comments on any anticipated or suspected overpressure zones

6.??? Technical issues encountered during the previous 24 hours and any corrective actions taken

7.??? Upcoming operations, including the planned drilling or logging operation, anticipated formations, and potential challenges

The wellsite geologist's concise and informative briefing keeps the drilling team well-informed and prepared for any potential geological challenges that may arise.

Q4. How do you estimate the net pay for your morning report on a quick-look basis?

Ans.? A wellsite geologist utilizes a combination of logs to estimate net pay on a quick-look basis in the following manner:

1.??? Establish a sand line on the gamma ray log to identify potential sandstone intervals

2.??? Determine a hydrocarbon cut-off on the resistivity log to distinguish hydrocarbon-bearing zones

3.??? Mark oil-bearing and gas-bearing reservoirs by analysing the GR, resistivity, neutron density cross-overs, and gas log.

4.??? Calculate the net pay thickness by summing the individual oil and gas pay intervals

5.??? Indicate possible oil pay and possible gas pay zones based on low resistivity, low porosity, or contamination in the lithology

This quick-look net pay estimation provides an initial assessment of the well's hydrocarbon potential and helps in further evaluation and decision-making processes.

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Q5. What is the effect of dolomitization on reservoir characteristics?

Ans.? Dolomitization is a diagenetic process that replaces calcium carbonate (calcite) with magnesium carbonate (dolomite) in sedimentary rocks. This process often enhances reservoir quality by increasing porosity and permeability.

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Q6. If we get a kick, what information will you pass to the operations geologist?

Ans. If a kick occurs, the wellsite geologist has to immediately inform the operations geologist and provide the following information:

1.??? Depth of the kick

2.??? Latest structural correlation of the wellbore

3.??? Events leading up to the kick, including ongoing operation, mud weight, gas readings and hole condition etc.

4.??? Duration and intensity of the drill break

5.??? Total gas and pit volume gain

6.??? Shut-in drill pipe pressure (SIDPP) and shut-in casing pressure (SICPP)

7.??? Estimated kill mud weight

8.??? Difference in formation pressure as per the kick and from logs/calculations

The idea is to be fully prepared with information and suggestion before you call town.

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Q7. What will be your concerns while drilling in an old field that has good quality clastic reservoirs?

Ans. Old oil and gas fields usually have depleted reservoirs which may present several challenges. Therefore we must anticipate:

1.??? Minor to moderate mud losses due to the pressure differential between the wellbore and the surrounding depleted formations

2.??? Differential sticking, if the hydrostatic and formation pressures differential is significant and depleted reservoirs are porous and permeable, we must seriously be concerned to avoid drillstring or wireline tools getting stuck

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Q8. After running the first set of electric logs, the wireline engineer gives you the printout. How will you QC the logs?

Ans.? Quality control (QC) of wireline logs is crucial to ensure the accuracy and reliability of the logs. The wellsite geologist should perform the following QC checks:

1.??? Verify the accuracy and completeness of information on the log heading including the scales on various tracks.

2.??? Examine the consistency of log curves, identify any missing or unusual patterns on the log curves that may indicate errors or inconsistencies.

3.??? Check that log calibrations are within the acceptable range and that any comments provided by the logging engineer are appropriate and informative.

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Q9. What are the various steps involved in taking a fluid sample on wireline?

Ans.? Collecting fluid samples using wireline tools provides valuable information about formation fluids and reservoir characteristics. The process typically involves the following steps:

1.??? Correlate the depth of the wireline tool with the geological formations encountered.

2.??? Position the wireline tool at the desired sampling depth and record the formation pressure.

3.??? Pump out to remove any contaminant (MF) until you see fresh reservoir fluids.

4.??? Identify fluid using OFA, resistivity and temperature.

5.??? Open the sample chamber and collect the fluid sample. ?

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Q10. How do you geosteer a directional well?

Ans. ?Geosteering is the process of controlling the trajectory of a directional wellbore to reach the desired target while maintaining wellbore stability and avoiding formation damage. The wellsite geologist plays a crucial role in geosteering by:

1.??? Plotting directional data on horizontal and vertical section plots to visualize the actual wellbore trajectory compared to the planned path.

2.??? Analysing the plotted trajectories to identify any deviations from the planned path and assess their severity.

3.??? Collaborating with operations geologist, company man and directional driller to make informed decisions about corrective actions, such as adjusting the toolface or reaming the wellbore.

4.??? Last but not least; communicating effectively with all stack holders is of paramount importance for successful well placement.

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